Fibrous sheet for structure reinforcement and structure reinforced with same

ABSTRACT

A fibrous sheet for structure reinforcement comprising a sheet layer of reinforcing continuous filament bundles (1) arranged parallelly spaced out from each other, auxiliary covering yarns (3, 4) arranged on both sides of the sheet layer in such a manner that each of the covering yarns intersects respective reinforcing filament bundles (1) while meandering along the longitudinal direction of the reinforcing filament bundles on at least one side of the sheet layer and auxiliary chain-stitching yarns (6) which interconnects the auxiliary covering yarns on one side of the sheet layer with the auxiliary covering yarns on the other side of the sheet layer through individual spaces among adjacent reinforcing filament bundles in a warp knitting structure.

TECHNICAL FIELD

The present invention relates to a fibrous sheet for structurereinforcement and a structure reinforced with the same. The presentinvention relates in more detail to a fibrous sheet for structurereinforcement most suitable for reinforcing not only general structuresbut also piers and floor systems of elevated structures, columns andwalls of buildings, and the like, and a structure reinforced with thesheet.

BACKGROUND ART

Social problems have recently arisen from the brittleness and durabilityof cement structures, for example, destruction of bridges caused byearthquakes, rust formation on reinforcing bars caused by theneutralization of concrete, the fatigue of reinforcing steels caused bya sharp increase in traffic volumes, and the like. Replacing thestructures with new ones is naturally satisfactory. However, replacingthem is very costly.

When a pier of an elevated structure is taken as an example, a methodfor reinforcing the pier by bonding a steel sheet to the columncontaining concrete with an adhesive and a method for reinforcing it bybonding sheet-like reinforcing layers containing carbon fibers have beenemployed as countermeasures. In particular, the latter method has cometo be adopted recently because the reinforced structures showsignificant reinforced effects and excellent durability, and because thereinforcing operation is simple. In the sheet-like reinforcing layerscontaining carbon fibers mentioned above, a number of carbon fibers arearranged in parallel in one or two directions. For example, JapanesePatent Kokai Publication Nos. 5-332031 and 7-243149 propose fibroussheets for structure reinforcement in which carbon fibers are arrangedin one direction. According to the former patent publication, carbonfiber bundles each containing a number of collected carbon fibers arearranged on an auxiliary sheet in one direction through an adhesivelayer. According to the latter patent publication, carbon fibers areunidirectionally pulled mutually in parallel and in a sheet-like mannerto form a sheet surface, and a weave structure is formed with transversedirection secondary fiber bundles and longitudinal direction secondaryfiber bundles parallel to the carbon fibers, both types of the bundlesbeing situated on respective sides of the sheet, to hold the sheet-likecarbon fiber bundle arranged in one direction.

Furthermore, Japanese Patent Kokoku Publication Nos. 57-52221 and8-23096 propose fibrous sheets for structure reinforcement in whichcarbon fibers are bidirectionally arranged.

According to the former patent publication, two carbon fiber bundles thecarbon fibers of which are pulled unidirectionally and mutually inparallel in a sheet-like manner within each bundle and which face eachother form a bidirectional sheet surface. The sheet surface is made toform a weave structure by longitudinal secondary fibers and transversesecondary fibers which are parallel to the respective fiber bundles, andis integrally held. According to the latter patent publication, a biasfabric is formed by a longitudinal carbon fiber bundle and a transversecarbon fiber bundle extending obliquely in relation to the longitudinalcarbon fiber bundle, and the carbon fibers are bidirectionally arrangedon the bias.

These unidirectional or bidirectional fibrous sheets for structurereinforcement are prepared to display the excellent high strength andhigh elastic modulus of the carbon fibers in the fiber axial directionas much as possible. Moreover, an auxiliary sheet and secondary fibersother than the carbon fibers are used to integrally hold the carbonfibers and obtain a fibrous sheet for structure reinforcement having adecreased fiber slippage within a sheet. That is, though a woven fabricis generally prepared by mutually intersecting warps and wefts to have adecreased fiber slippage, the constituent fibers are markedly bent atthe intersectioning points of the warps and wefts. As a result, when astress is applied to the fabric, the stress is concentrated at the bentportions, and in a woven fabric consisting of carbon fibers, theinherent high strength and high elastic modulus of carbon fibers cannotbe displayed.

However, in spite of the improvement of the fibrous sheet for structurereinforcement as described above, a coarse fibrous sheet for structurereinforcement having a decreased fiber slippage, a high toughnessunidirectionally or bidirectionally and numerous spaces amongreinforcing fibers in a sheet is not obtained currently. To reinforce,for example, a column containing concrete by the use of the fibroussheets for structure reinforcement, the concrete to be reinforced isfirst coated with an adhesive and the concrete is subsequently woundwith the fibrous sheet while the sheet is being pressed, followed bycoating the fibrous sheet with an adhesive to form a reinforcing layer.In order to make the fibrous sheet for structure reinforcement functionas a reinforcement layer, it is important that the adhesive shouldpenetrate sufficiently among fibers within each of the fiber bundles andamong the fiber bundles. To meet the requirement, the fibrous sheet forstructure reinforcement must have spaces the adhesive can penetrateamong the reinforcing fibers forming the fibrous sheet, namely amongfibers within each of the fiber bundles and among the fiber bundles. Ingeneral, when the spaces among the fibers in the fibrous sheet forstructure reinforcement become large, there arise problems that theslippages among fibers become large and that the toughness falls in thearrangement direction of the fibers. Accordingly, the fibrous sheet forstructure reinforcement can fulfill its role as a reinforcing layer of amember to be reinforced only after the fibrous sheet sufficiently meetsthe three requirements mentioned above.

Disclosure of Invention

An object of the present invention is to solve the problems associatedwith the prior art as mentioned above, and provide a fibrous sheet forstructure reinforcement which has a decreased slippage within the sheet,a high toughness in the arranged directions of the fibers (one or twodirections), numerous spaces among fibers and good penetration of anadhesive, as a fibrous sheet for reinforcing not only general structuresbut also piers of elevated structures, columns and walls of buildings,and the like, which also facilitates handling during execution of worksand which has lightness of the reinforcing layer, and a structurereinforced with the sheet.

The present inventors have intensively conducted investigation to meetthe following requirements simultaneously so that the above object isachieved: prevention of fiber slippage within the fibrous sheet forreinforcement, high toughness in the arranged direction of the fibers,and numerous spaces among fibers. As a result, they have elucidated thatthe problems can be solved only after adopting a specific warp knittingstructure.

That is, according to the present invention, the following fibrous sheetfor structure reinforcement is provided.

A fibrous sheet for structure reinforcement comprising

a sheet layer of reinforcing continuous filament bundles arrangedparallelly spaced out from each other,

auxiliary covering yarns arranged on both sides of said sheet layer insuch a manner that each of said covering yarns intersects respectivereinforcing filament bundles while meandering along the longitudinaldirection of said reinforcing filament bundles on at least one side ofsaid sheet layer, and

auxiliary chain-stitching yarns which interconnects the auxiliarycovering yarns on one side of said sheet layer with the auxiliarycovering yarns on the other side of said sheet layer through individualspaces among adjacent reinforcing filament bundles in a warp knittingstructure.

Furthermore, according to the present invention, the following structureis provided.

A structure formed by covering a structure member to be reinforced withthe fibrous sheet for structure reinforcement as mentioned above in theperipheral and/or longitudinal direction through an adhesive.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(A) and 1(B) are enlarged fragmentary schematic views showing anexample of a fibrous sheet for structure reinforcement of the presentinvention in which reinforcing continuous filaments are unidirectionallyarranged. FIG. 1(A) and FIG. 1(B) show the front side and the back sideof the sheet, respectively.

FIGS. 2(A) and 2(B) are enlarged fragmentary schematic views showing anexample of a fibrous sheet for structure reinforcement of the presentinvention in which reinforcing continuous filaments are unidirectionallyarranged. FIG. 2(A) and FIG. 2(B) show the front side and the back sideof the sheet, respectively.

FIGS. 3(A) and 3(B) are enlarged fragmentary schematic views showing anexample of a fibrous sheet for structure reinforcement of the presentinvention in which reinforcing continuous filaments are bidirectionallyarranged. FIG. 3(A) and FIG. 3(B) show the front side and the back sideof the sheet, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

In a unidirectional fibrous sheet for structure reinforcement in FIG.1(A), reinforcing continuous filaments are arranged to form a filamentbundle (1) as a unit. Such filament bundles (1, 1', 1", - - - ) arearranged in a rib-shaped form with spacings (5, 5', 5", - - - ). On thefibrous sheet, auxiliary covering yarns (3) are arranged in such amanner that they intersect the respective rib-shaped filament bundles(1) while meandering along the longitudinal direction thereof whereinthe tips of meandering exist in rib-to-rib spaces. The covering yarns(3) are each interconnected with auxiliary chain-stitching yarn (6)through rib-to-rib spaces (5) among adjacent filament bundles in a warpknitting structure. On the other hand, on the back side of the sheet, asshown in FIG. 1(B), other auxiliary covering yarns (4) which intersectthe respective rib-shaped filament bundles (1) on the back side of thebundles while meandering are each interconnected with auxiliarychain-stitching yarn (6) used in common with the yarn on the front side,through rib-to-rib spaces (5) among adjacent filament bundles in a warpknitting structure used in common with the structure on the front side.

On the other hand, in a unidirectional fibrous sheet for structurereinforcement in FIGS. 2(A) and 2(B), an auxiliary covering yarn (e.g.,3 or 4) is arranged in such a manner that it intersects two adjacentrib-shaped filament bundles (e.g., 1 and 1') while meandering along thelongitudinal direction of the bundles. Moreover, the covering yarn (3 or4) is interconnected with auxiliary chain-stitching yarn (6) used incommon on the front and back surfaces in a warp knitting structurethrough rib-to-rib spaces (5 and 5") on both sides of the two adjacentfilament bundles.

That is, the fibrous sheet for structure reinforcement shown in FIGS.1(A) and 1(B) or FIGS. 2(A) and 2(B) has a structure in which thereinforcing continuous filament bundles appear to be inserted into ameshed bag-like warp knitting structure consisting of the covering yarns(3, 4) and the chain-stitching yarn (6). The reinforcing filamentbundles are prevented from forming slippages within the fibrous sheet bythe meshed bag-like warp knitting structure. Moreover, since there arethe rib-to-rib spaces (5) among adjacent reinforcing filament bundles,the fibrous sheet exhibits easy impregnation with resin. Furthermore,since the continuous filament bundles (1, 1', 1" - - - ) are arranged ina rib-shaped form, the strength in the arranged direction is extremelyhigh. In particular, when the covering yarns are arranged in such amanner as shown in FIGS. 2(A) and 2(B), the fibrous sheet has advantagesas described below. The reinforcing filament bundles are prevented fromforming slippages within the sheet even when the chain-stitching yarn iscut. The flexural rigidity of the sheet is improved, and the easyhandling of the sheet during execution of works is improved.Accordingly, the arrangement is particularly preferred.

On the front side of a bidirectional fibrous sheet for structurereinforcement shown in FIG. 3(A), reinforcing continuous filamentbundles (1, 1', 1" - - - ) consisting of reinforcing continuousfilaments, auxiliary covering yarns (3), auxiliary chain-stitching yarn(6) located in rib-to-rib spaces (5) of the filament bundles and a warpknitting structure with the auxiliary yarns (3, 6) are similar in thefibrous sheet in FIG. 1(A). On the other hand, on the back side of thefibrous sheet, reinforcing continuous filament bundles (2, 2', 2", 2'",2"" - - - ) consisting of the same reinforcing continuous filaments asthose forming the reinforcing continuous filament bundles (1, 1',1" - - - ) are inserted as wefts in a rib-shaped form so that thefilament bundles fulfill the role of the auxiliary covering yarns (4) inFIG. 1(B). The filament bundles inserted as wefts are interconnectedwith the auxiliary chain-stitching yarn (6) used in common on the frontside in a warp knitting structure used in common on the front side.

That is, the fibrous sheet for structure reinforcement shown in FIGS.3(A) and 3(B) has a structure in which the reinforcing continuousfilament bundles appear to be inserted into a warp knitting structureconsisting of the auxiliary covering yarns (3) and the auxiliarychain-stitching yarn (6) by warp (1, 1', 1" - - - ) insertion and weft(2, 2', 2", 2'", 2"" - - - ) insertion. The two groups of the continuousfilament bundles (1 - - - , 2 - - - ) face each other to form abidirectional sheet surface.

Accordingly, the fibrous sheet composed of the bidirectional filamentbundles is prevented from forming slippages of the filament bundleswithin the sheet. Moreover, since there are spaces in the filamentbundles, the fibrous sheet is easily impregnated with a resin, and fullydisplays the strength of the reinforcing continuous filaments in the twodirections.

Although the fibrous sheets for structure reinforcement in the presentinvention have specific warp knitting structures as mentioned above, asessential requirements, the following construction requirements for thereinforcing continuous filaments, auxiliary yarns, warp knittingstructures and fibrous sheets are preferably and suitably selected.

In the filament bundles in which the reinforcing continuous filamentsare arranged in parallel, the tensile strength of the reinforcingcontinuous filaments is preferred to be at least 20 g/de in view of thestrength of the fibrous sheet for structure reinforcement. Moreover, thesingle filament size is preferred to be from 0.1 to 10 denier and morepreferred to be from 0.1 to 2.0 denier in view of the resin impregnationinto the fibrous sheet for structure reinforcement. When theserequirements are satisfied, various fibers such as polyethylene fibers,carbon fibers, glass fibers and aramid fibers can be selected. Among thefibers, the aramid filaments are particularly preferred, andcopoly-p-phenylene-3,4'-oxydiphenyleneterephthalamide (trade nameTechnola, manufactured by Teijin Ltd.) is particularly preferred becauseit has not only a high strength but also a high elongation. Moreover,the size of one unit of the filament bundles is preferred to be 1,000 to50,000 denier in view of the strength. Furthermore, the number of thefilament bundles in the width direction of the fibrous sheet, namely thewarp density is preferred to be from 3 to 18 bundles/inch in view of thestrength and the impregnation of the resin.

Furthermore, the size and the tensile strength of the auxiliary yarns(covering yarns and chain-stitching yarn) forming the warp knittingstructure which is used for preventing formation of the slippages of thereinforcing filaments are preferred to be from 50 to 3,000 denier and atleast 3.0 g/de, respectively in view of the good knittingprocessabilities, the effects of preventing the slippage formation ofthe reinforcing filaments within the sheet and the prevention of thebreakage of the auxiliary yarns during execution of works.

The auxiliary yarns can be suitably selected from natural fibers,semi-synthetic fibers and synthetic fibers so long as the selectedfibers satisfy the requirements. Polyvinyl alcohol yarns and polyesteryarns are particularly preferred.

The weft density in the warp knitting structure (namely, number of loopsper inch of the auxiliary covering yarns arranged while meandering alongthe longitudinal direction of the reinforcing filament bundles) ispreferred to be from 3 to 25 courses/inch in view of the prevention ofthe slippage formation of the reinforcing filaments and the impregnationof the resin.

Furthermore, the weight of the fibrous sheet containing the reinforcingfilaments and the auxiliary yarns is preferred to be from 100 to 2,000g/m² in view of the strength, easy handling and lightness.

The fibrous sheet for structure reinforcement of the present inventioncan be easily manufactured by modifying general raschel warp knitting.Formation of the warp knitting structure with the auxiliary coveringyarns and auxiliary chain-stitching yarn is conducted in accordancewith, for example, a technique published in Knowledge of New Fibers,Kamakura Shobo, 104-107, revised 3rd edition (1994). In addition, thefibrous sheets in FIGS. 1(A) and 1(B) and FIGS. 2(A) and 2(B) have beenmanufactured with a warp knitting machine with a 4-bar construction, andthe fibrous sheet in FIGS. 3(A) and 3(B) has been manufactured with awarp knitting machine having a 3-bar construction by conducting weftinsertion. For example, the fibrous sheet for structure reinforcement inFIGS. 1(A) and 1(B) can be easily manufactured by setting from the upperside the auxiliary chain-stitching yarns (6), the auxiliary coveringyarns (3), the reinforcing filaments (1) and the auxiliary coveringyarns (4) on the creels for the warp knitting machine, and supplying thefilaments and yarns to a raschel warp knitting machine from the creels.Moreover, the fibrous sheet can also be prepared by stacking at leastone layer in the thickness direction along the warp and/or weft. Forexample, the fibrous sheet in FIGS. 1(A) and 1(B) is incorporated intothe fibrous sheet in FIGS. 3(A) and 3(B) to give a structure wherein thereinforcing filaments form a 3-layered sheet plane consisting of thewarp directional layer, weft directional layer and warp directionallayer, the auxiliary covering yarns are arranged on the first and thirdlayers, said covering yarns thereon are interconnected with theauxiliary chain-stitching yarn in the warp knitting structure, and thereinforcing filaments in the weft direction become sandwich-likecontents. The warp knitting machine has a 5-bar construction at thistime, and wefts are inserted thereinto.

In the present invention, a structure member to be reinforced is coveredwith the fibrous sheet for structure reinforcement in the peripheraland/or longitudinal direction through an adhesive to form a reinforcedstructure.

A specific procedure for reinforcing a structure member to be reinforcedusing the fibrous sheet for structure reinforcement is as describedbelow. For example, when a concrete column is to be reinforced, thesurface of the structure member is cleaned, and peelable surface layersare removed. The structure member is coated with a primer to increasethe adhesion of an adhesive. The structure member is further coated withan adhesive using a brush, a roller, a trowel, or the like. The primerand adhesive can be selected from the kinds of epoxy, urethane, ester,and the like. Moreover, the primer and the adhesive may be of the sametype or different type, and they are particularly preferred to be ofepoxy-based ones. Furthermore, since the temperature and humidity varydepending on the season when the reinforcement is practiced, it isneedless to say that the specification (e.g. solvent, viscosity, curingagent) of the epoxy-based primer and adhesive may be changed inaccordance with the season.

After coating the structure member to be reinforced with an adhesive,the fibrous sheet for structure reinforcement is laminated. Thestructure member is wound with the fibrous sheet on the peripheralsurface while the fibrous sheet is being pulled in the horizontaldirection, and the fibrous sheet thus wound is pressed with a roller,etc. to be entirely bonded. In the fibrous sheet for structurereinforcement used in the present invention, the warp knitting structureformed by the auxiliary fibers prevents the reinforcing filamentscontained in the fibrous sheet from forming slippages. The fibroussheet, therefore, is not expanded greatly even when a tensile stress isapplied thereto in the horizontal direction to some degree duringlaminating. The fibrous sheet can, therefore, be well handled, anduniformly laminated. Moreover, since spaces are formed among reinforcingbundles, the adhesive is squeezed out of the filaments when the fibroussheet is pressed with a roller, whereby the fibrous sheet for structurereinforcement is completely conformable to the adhesive layer.

After bonding the fibrous sheet to the entire outer periphery of thecolumn from the upper end to the lower end is finished, an adhesive isapplied to the bonded first fibrous sheet, and a second layer of thefibrous sheet is laminated. The procedure is repeated, and the fibroussheets are bonded up to a maximum of 10 layers. Even when the fibroussheets are laminated in an amount exceeding 10 layers, the reinforcingeffects are the same as in 10 layers.

As explained above, the fibrous sheets for structure reinforcement arelaminated to the structure member to be reinforced, and the outermostlaminated sheet is coated with a resin mortar if necessary painted toform a surface protective layer. A sheet (a woven or knitted fabrichaving loops on the surface or a fibrous composite structure prepared bylaminating an unwoven fabric to a mesh woven fabric) for bonding themortar layer is preferably placed between the outermost sheet layer andthe resin mortar. That is, the outermost sheet is coated with theadhesive, and the sheet for bonding the mortar layer is laminated to theoutermost sheet, followed by applying the resin mortar. The resin mortarentraps the sheet for bonding the mortar layer to be integrated. Theconstraint force between the resin mortar and the sheet for bondingprevents crack formation in the resin mortar.

The method for reinforcing a structure member as explained above indetail is one which reinforces the structure member to be reinforcedsuch as a concrete column by covering the structure member entirely fromthe upper end to the lower end in the peripheral and/or longitudinaldirections. It is needless to say that the structure member maynaturally be reinforced locally in the peripheral direction alone, andthat the fibrous sheet for structure reinforcement may also be laminatedin a flat form (namely, without winding) to a flat member such as afloor system and a wall in accordance with the shape.

In reinforcing a structure member to be reinforced using the fibroussheet for structure reinforcement of the present invention, thereinforcing continuous filaments of the fibrous sheet, having a highstrength and a high elastic modulus are naturally optimum. Carbon fiberssurely satisfy the requirements from such a standpoint. However, severalproblems are pointed out in reinforcing a column composed of, forexample, concrete, using the carbon fiber sheet. One of the problems isthat since the carbon fibers have a low elongation and are lesselongated, reinforcing an acute portion of the structure member must beconducted after chamfering the portion so that it has an obtuse angle ora smooth shape.

On the other hand, since aramid (aromatic polyamide) fibers have a highstrength and a high elastic modulus and are elongated more than thecarbon fibers, the chamfering operation is not necessary, and the aramidfibers have come to be adopted for reinforcement recently from thestandpoint of improving the workability. However, it has heretofore beenpointed out that the aramid fibers have a poor weatherability comparedwith other fibers. In reinforcing a column composed of, for example,concrete using an aramid fibrous sheet, the durability of reinforcementwith the aramid fibrous sheet is feared when cracks are formed in thefinishing layer (mortar or paint) after reinforcement. Concerning thereinforcement by covering with an aramid fibrous sheet, it is,therefore, preferred that at least the outermost layer of the coveredfibrous sheets for structure reinforcement be impregnated with anadhesive containing a UV stabilizer and bonded with the adhesive. The UVstabilizer herein refers to an agent added for the purpose of protectingthe aramid fibers forming the aramid fibrous sheet from beingdeteriorated as a result of absorbing UV rays (wavelength: 380 nm). TheUV stabilizer is, for example, a general UV absorbing agent such ascarbon and titanium dioxide. The UV stabilizer is added to the adhesivein an amount of 0.75 to 5.0% by weight, preferably 0.75 to 2.0% byweight. Moreover, the adhesive layer containing the UV stabilizer isformed on the fibrous sheet for structure reinforcement to have athickness of 150 to 700 mμ, preferably 200 to 700 mμ. When the amount ofthe UV absorber is less than 0.75% by weight, or the thickness of theadhesive layer is less than 150 mμ, significant effects of weatheringresistance cannot be obtained. When the amount of the UV absorberexceeds 5.0% by weight, or the thickness of the adhesive layer exceeds700 mμ, the effects are the same as in 5.0% by weight or 700 mμ layer.

Industrial Applicability

Since reinforcing continuous filaments having a high strength in thefibrous sheet for structure reinforcement of the present invention arearranged with spaces within the sheet by specific warp knittingstructure with auxiliary yarns, the following advantages are obtained:there are no slippages of the reinforcing continuous filaments withinthe sheet, the sheet shows good impregnation of the resin owing to thepresence of spaces among the filaments, and the sheet shows a sufficientstrength in the arranged direction of the filaments. Accordingly, bybeing impregnated with a resin, the sheet is useful for reinforcing notonly general structures but also piers and floor systems of elevatedstructures, columns and walls of buildings, and the like. Moreover thesheet is excellent in easy handling and lightness during execution ofworks, and since a reinforced structure has a high tensile strength anda high shear strength, it has, therefore, an extremely high industrialvalue as a reinforced structure compared with other materials.

The present invention will be further illustrated with reference to thefollowing examples. However, the scope of the present invention is by nomeans restricted by these examples.

In addition, the properties of the sheets in the examples are evaluatedon the basis of the criteria mentioned below.

Knitting processability The knitting processability is evaluated fromthe number of stops of the knitting machine, per 100 m during formingthe fibrous sheet in a warp knitting structure and the results are shownby the following criteria:

    ______________________________________                                               less than 5 times                                                                        ⊚                                              from 5 to 10 times ∘                                              from 10 to 30 times Δ                                                   at least 30 times x                                                         ______________________________________                                    

Appearance quality of sheets The appearance quality of a sheet isevaluated from number of defects (slippages, fluffs, broken threads) per25 m² of the fibrous sheet and the results are shown by the followingcriteria:

    ______________________________________                                               less than 10                                                                           ⊚                                                from 10 to 20 ∘                                                   from 20 to 40 Δ                                                         at least 40 x                                                               ______________________________________                                    

Impregnation of resin: Using an adhesive (article No. A20, trade name ofAR Bond, manufactured by Teijin Ltd.), the epoxy resin and the curingagent are mixed in a ratio of 2:1. A concrete is coated with theadhesive and a sheet is bonded to the concrete by the adhesive thusobtained so that the adhesion force between them becomes 30 kgf/cm² (inaccordance with JIS A6916). The impregnation is evaluated from theamount of the adhesive for the adhesion force between them becoming 30kgf/cm², and the evaluation criteria are as follows:

    ______________________________________                                        the amount of adhesive                                                                           small    ⊚                                     medium ∘                                                          large Δ                                                                 very large x                                                               ______________________________________                                    

EXAMPLES 1 to 10

Among copoly-p-phenylene-3,4'-oxydiphenyleneterephthalamide fibers(trade name Technola, manufactured by Teijin Ltd.), continuous filamentshaving a single filament denier of 1.5 denier, a strength of 28 g/de andsizes as shown in Table 1 were used as reinforcing continuous filaments.Moreover, among groups of polyethyeleneterephthalate fibers (trade nameTetron, manufactured by Teijin Ltd.), those groups having a strength of5.0 g/de and sizes shown in Table 1 were used as auxiliary coveringyarns and auxiliary chain-stitching yarn. The chain-stitching yarn,covering yarns, reinforcing filaments and covering yarns were set on thecreels in this order from the upper side, and supplied to a raschel warpknitting machine (4 bar construction, chain-stitched structure). Thewarp density of the reinforcing filament bundles and the weight of thefibrous sheet were varied during the preparation as shown in Table 1 toobtain fibrous sheets for structure reinforcement. The fibrous sheetsthus obtained had a structure as shown in FIGS. 1(A) and 1(B), and thereinforcing continuous filaments were unidirectionally arranged to forma single layer alone. Table 1 shows the evaluation results of theknitting processabilities of the fibrous sheets, the appearance qualityof the sheets such as slippages and impregnation of the epoxy resin.

EXAMPLES 11 to 16

The characteristics (size and density) of the filament bundles composedof reinforcing filaments or the weft density of the warp knitting inExample 3 were changed as shown in Table 2 to obtain fibrous sheets forstructure reinforcement. The fibrous sheets were evaluated in the samemanner as in Example 3, and the results thus obtained are listed inTable 2.

EXAMPLES 17 to 19

Auxiliary chain-stitching yarn, auxiliary covering yarns and reinforcingfilaments (both of yarns and filaments same as in example 3) were set onthe creels in this order from the upper side, and supplied to a raschelwarp knitting machine (3 bar construction). At this time, continuousfilament bundles composed of the above reinforcing continuous filamentsand having a size of 4,500 de were weft-inserted as auxiliary coveringyarns on the back side. The fibrous sheet thus obtained had a structureas shown in FIGS. 3(A) and 3(B). Table 2 also shows the evaluationresults of the fibrous sheets as a function of the density of thefilament bundles and the weft density of the warp knitting structure.

                                      TABLE 1                                     __________________________________________________________________________                          Ex. 1                                                                            Ex. 2                                                                            Ex. 3                                                                            Ex. 4                                                                             Ex. 5                                      __________________________________________________________________________      Reinforcing Size of filament de 800 1200 7500 45000 52000                     filaments bundles                                                              Warp density of bundles/ 18 18 9 9 9                                          filament bundles inch                                                        Auxiliary Size de 200 200 200 200 200                                         yarns                                                                         Structure Weft density courses/inch 15 15 15 15 15                             Weight g/m.sup.2 98 130 330 1800 2100                                        Sheet Warp strength of ton/10 cm 1.4 2.1 6.6 39 46                            properties sheet                                                               Warp elongation of % 5 5 5 5 5                                                sheet                                                                         Knitting ⊚ ∘ Δ x ⊚                                            ⊚ ⊚                                             ∘ ∘                   processability                                                                Appearance qulaity ⊚ ∘ Δ x .circleinci                                       rcle. ⊚ ⊚                                        ∘ ∘                  of sheet                                                                      Impregnation of ⊚ ∘ Δ x .circleincircl                                       e. ⊚ ⊚                                          ∘ Δ                         resin                                                                      __________________________________________________________________________         Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10                                           __________________________________________________________________________      Reinforcing Size of filament de 7500 7500 7500 7500 7500                      filaments bundles                                                              Warp density of bundles/ 9 9 9 9 9                                            filament bundles inch                                                        Auxiliary Size de 40 60 200 800 1200                                          yarns                                                                         Structure Weft density courses/inch 15 15 15 15 15                             Weight g/m2 300 306 330 435 506                                              Sheet Warp strength of ton/10 cm 6.1 6.5 6.6 6.6 6.6                          properties sheet                                                               Warp elongation % 5 5 5 5 5                                                   of sheet                                                                      Knitting ⊚ ∘ Δ x ∘                                               ∘ ⊚                                                ⊚ ⊚                                               processabiiity                              Appearance ⊚ ∘ Δ x Δ .smallcircl                                       e. ⊚ ⊚                                          ∘                                 quality of sheet                                                              Impregnation of ⊚ ∘ Δ x .circleincircl                                       e. ⊚ ⊚                                          ∘ Δ                         resin                                                                      __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                         Ex. 11                                                                            Ex. 12                                                                            Ex. 13                                                                            Ex. 14                                                                            Ex. 15                                   __________________________________________________________________________      Reinforcing Size of filament de 30000 4500 4500 7500 7500                     filament bundles                                                               Warp density of bundles/ 2 18 20 9 9                                          filament bundles inch                                                        Auxiliary Size de 200 200 200 200 200                                         yarns                                                                         Structure Weft density courses/inch 15 15 15 2 23                              Weight g/m 290 404 410 308 358                                               Sheet Warp strength of ton/10 cm 5.4 7.9 8.7 5.9 6.6                          properties sheet                                                               Warp elongation % 5 5 5 5 5                                                   of sheet                                                                      Weft strength of ton/10 cm -- -- -- -- --                                     sheet                                                                         Weft elongation % -- -- -- -- --                                              of sheet                                                                      Knitting ⊚ ∘ Δ x Δ ∘                                          Δ Δ ⊚                                               processability                            Appearance ⊚ ∘ Δ x Δ .smallcircl                                         e. Δ Δ ⊚                                             quality of sheet                          Impregnation of ⊚ ∘ Δ x ∘                                          ∘ Δ ∘                                           ∘                               resin                                                                      __________________________________________________________________________                           Ex. 16                                                                            Ex. 17                                                                             Ex. 18                                                                            Ex. 19                                    __________________________________________________________________________      Reinforcing Size of filament de 7500 7500 7500 7500                           filaments bundles                                                              Warp density of bundles/ 9 6 9 15                                             filament bundles inch                                                        Auxiliary Size de 200 200 200 200                                             yarns                                                                         Structure Weft density courses/inch 27 10 15 25                                Weight g/m.sup.2 363 430 625 1055                                            Sheet Warp strength of ton/10 cm 6.6 4.4 6.6 11                               properties sheet                                                               Warp elongation of % 5 5 5 5                                                  sheet                                                                         Weft strength of ton/10 cm -- 4.4 6.6 11                                      sheet                                                                         Weft elongation of % -- 5 5 5                                                 sheet                                                                         Knitting ⊚ ∘ Δ x ∘                                                ⊚ ⊚                                             ⊚                             processability                                                                Appearance quality ⊚ ∘ Δ x .smallcircl                                        e. ⊚ ⊚                                          ∘                                of sheet                                                                      Impregnation of ⊚ ∘ Δ x Δ                                               ⊚ ⊚                                             ∘                                resin                                                                      __________________________________________________________________________

From the evaluation results in Examples 1 to 19, conclusions asdescribed below can be drawn. To comprehensively satisfy the knittingprocessability, appearance quality and impregnation of the fibrous sheetfor structure reinforcement of the present invention, it is preferredthat the following conditions be satisfied: the size o f the filamentbundles of the reinforcing continuous filaments is from 1,000 to 50,000denier, the warp density thereof is from 3 to 18 bundles/inch, the sizeof the auxiliary yarns is from 50 to 1,000 denier, the weft density ofthe warp knitting structure is from 3 to 25 courses/inch, and the weightof the fibrous sheet is from 100 to 2,000 g/M².

EXAMPLES 20 to 21

A reinforced concrete member having a square section (side length: 90cm) and a length of 3 m was wound with the aramid fibrous sheet forstructure reinforcement having sheet properties in Example 3 three timesover the entire periphery from the upper end to the lower end, throughan epoxy adhesive (article No. A20, trade name of AR Bond, manufacturedby Teijin Ltd., ratio of epoxy curing agent=2:1) to be covered andreinforced. During the winding operation, the outermost layer was coatedwith the epoxy adhesive in which 1.0% of a UV stabilizer (weight ratioof titanium dioxide/carbon of 100:3) had been added, and the resinthickness was 350 μm (Example 20). Alternatively, the outermost layerwas coated with the epoxy resin containing no UV stabilizer, and theresin thickness was 700 μm (Example 21). The covered reinforced concretemembers having no surface protective layer (resin mortar) were allowedto stand outdoors for 1 year. The concrete member prepared in Example 20showed no substantial appearance change, whereas the one prepared inExample 21 showed discoloration of the resin layer and was somewhatembrittled.

We claim:
 1. A fibrous sheet for structure reinforcement comprisingasheet layer of reinforcing continuous filament bundles arrangedparallelly spaced out from each other; said reinforcing continuousfilaments having a tensile strength of at least 20 g/de, auxiliarycovering yarns arranged on both sides of said sheet layer in such amanner that each of said covering yarns intersects respectivereinforcing filament bundles while meandering along the longitudinaldirection of said reinforcing filament bundles on at least one side ofsaid sheet layer, and auxiliary chain-stitching yarns which interconnectthe auxiliary covering yarns on one side of said sheet layer with theauxiliary covering yarns on the other side of said sheet layer throughindividual spaces among adjacent reinforcing filament bundles in a warpknitting structure.
 2. The fibrous sheet for structure reinforcementaccording to claim 1, wherein either one of said auxiliary coveringyarns is reinforcing continuous filament bundles of the same reinforcingcontinuous filaments as those forming said reinforcing continuousbundles and inserted as wefts in the warp knitting structure.
 3. Thefibrous sheet for structure reinforcement according to claim 1 or 2,wherein the warp density of said bundles is from 3 to 18 bundles/inch.4. The fibrous sheet for structure reinforcement according to any one ofclaims 1 or 2, wherein the weft density of the warp knitting structureis from 3 to 25 courses/inch.
 5. The fibrous sheet for structurereinforcement according to any one of claims 1 oe 2, wherein the size ofsaid auxiliary yarns is from 50 to 3,000 denier.
 6. The fibrous sheetfor structure reinforcement according to claim 5, wherein the tensilestrength of said auxiliary yarns is at least 3.0 g/de.
 7. The fibroussheet for structure reinforcement according to any one of claims 1 or 2,wherein the size of said bundles is from 1,000 to 50,000 denier.
 8. Thefibrous sheet for structure reinforcement according to any one of claims1 or 2, wherein the single filament size of said reinforcing continuousfilaments is from 0.1 to 10 denier.
 9. The fibrous sheet for structurereinforcement according to any one of claims 1 or 2, wherein thereinforcing continuous filaments are aramid filaments.
 10. The fibroussheet for structure reinforcement according to claim 9, wherein thereinforcing continuous filaments are aramid filaments composed ofcopoly-p-phenylene-3,4'-oxydiphenyleneterephthalamide.
 11. The fibroussheet for structure reinforcement according to any one of claims 1 or 2,wherein the weight of the fibrous sheet is from 100 to 2,000 g/m².
 12. Astructure formed by covering a structure member to be reinforced withthe fibrous sheet for structure reinforcement according to any one ofclaims 1 or 2 in the periphery and/or longitudinal direction through anadhesive.
 13. The structure according to claim 12, wherein the structureis formed by winding the structure member to be reinforced with thefibrous sheet for structure reinforcement in at least the periphery 1 to10 times through an adhesive.
 14. The structure according to claim 12,wherein the structure is formed by covering the structure member to bereinforced with the fibrous sheet for structure reinforcement in thelongitudinal direction 1 to 10 times through an adhesive withoutwinding.